Graptolitos del Tremadociense (Ordovícico Inferior) de la Formación Volcancito, Sistema de Famatina (La Rioja, Argentina)

Abstract

El Miembro Peña Negra de la Formación Volcancito (Tremadociense) del Sistema de Famatina (noroeste argentino) consta de pizarras negras graptolíticas, que se investigaron paleontológicamente, capa a capa, a lo largo de 400 m de sucesión en las secciones complementarias de Peña Negra y río Volcancito, la segunda de las cuales incluye los niveles más modernos. Los resultados bioestratigráficos permiten una correlación precisa con las asociaciones evolutivas y cronozonas globales de graptolitos del Tremadociense, y la reevaluación de todas las dataciones e identificaciones previas de la unidad. Los graptolitos más antiguos se localizan en el Miembro Filo Azul de la formación (Cámbrico Superior-Tremadociense) y se adscriben muy probablemente a la cronozona de Rhabdinopora flabelliformis parabola de la base del Ordovícico, lo que concuerda con los datos suministrados por los trilobites y conodontos. Desde el punto de vista paleontológico, se identifican y describen Rhabdinopora fl abelliformis flabelliformis, R. f. anglica, R. f. socialis, R. f. bryograptoides?, R. cf. enigma, Anisograptus matanensis y Bryograptus? sp. La forma Rhabdinopora flabelliformis famatinensis se propone restringirla al holotipo para obviar su mala caracterización taxonómica. Las nuevas formas Rhabdinopora turneri sp. nov. y R. flabelliformis acenolazai subsp. nov., guardan ciertas similitudes con los graptolitos planctónicos R. praeparabola y R. flabelliformis parabola, respectivamente. Sin embargo, los nuevos taxones del Famatina coexisten en horizontes más modernos de las cronozonas de A. matanensis y R. f. anglica, que claramente postdatan la aparición del desarrollo proximal trirradiado.

Middle Ordovician trilobites from the Castillejo Formation, Eastern Iberian Range (NE Spain): taxonomic reappraisal, biostratigraphy, and correlation

“…The overlying middle or Alpartir Member (110-200 m thick) is mainly composed of shales with some intercalations of sandstones and siliceous and ferruginous nodules. Graptolites of the D. murchisoni Zone have been found up to 25-30 m above the base of this member (Gutiérrez-Marco, 1986), being indicative of the uppermost Oretanian (ca. lower Dw3 of the global scale, Bergström et al, 2009).…”

“…204a-204b, respectively). The general geological mapping of the Eastern Iberian Chain at a scale of 1:50,000 provided some new data on Middle Ordovician trilobites, belonging both to original finds (the citation of "Calymene tristani" near Alpartir made by Hernández Samaniego et al, 1980), as well as a transliteration of the data collected by Hammann (1983) plus several unpublished MSc and PhD dissertations carried out in this area and mentioned in their explanatory notes: Kolb (1978), Gaubatz (1981), Keller (1981), Kistner (1981) and Gutiérrez-Marco (1980, 1986. This is the case of Hernández et al (1983a), who cited three horizons with trilobites in the Castillejo Formation near Fombuena:…”

Darriwilian (Middle Ordovician) graptolites from Sierra de Lina and Cauchari, Argentine Puna

“…These complexes include sequences associated with silicic volcanism covered by volcanoclastic turbidites (Bahlburg et al, 1990). The Puna Turbidite Complex comprises successions up to 3500 m stratigraphically thick, of Dapingian–Darriwilian age, according to graptolite records (Bahlburg et al, 1990; Gutiérrez‐Marco et al, 1996; Monteros et al, 1996; Ortega et al, 2011; Toro et al, 2003). The thick stratigraphic successions of marine origin correspond to the Lina, Falda Ciénaga and Coquena formations, defined by Ramos (1972), F. Aceñolaza et al (1976) and Schwab (1973), respectively.…”

“…The Huaytiquina section, close to the international Argentina/Chile boundary (Figure 1), contains graptolites of the Azygograptus lapworthi and Isograptus victoriae zones, of early Dapingian age, recovered from lower‐middle levels of the Coquena Formation (Monteros et al, 1996; Toro & Herrera Sánchez, 2019). A succession referable to the lower Darriwilian was studied in the Cuesta del Toquero at Tafna locality, close to the border with Bolivia, where Gutiérrez‐Marco et al (1996) described a graptolite assemblage with Pendeograptus pendens liber (Carter) as the dominant species, Aulograptus climacograptoides (Bulman), dichograptids, sigmagraptids and biserial graptolites, between others, referred to the Levisograptus austrodentatus Zone. The occurrence of Didymograptus artus Elles and Wood and biserial graptolites in the Esquina Colorada section recorded by Bahlburg et al (1990) suggest a similar age.…”

“…Studies on Middle Ordovician graptolites in the Puna have been increasing from the first record of Didymograptus climacograptoides Holm [= Aulograptus climacograptoides (Bulman)] by Loss (1949) in the Tafna locality, west of the La Quiaca city, Jujuy Province (Argentina/Bolivia boundary). The works of Ramos (1972), F. G. Aceñolaza and Durand (1975), F. G. Aceñolaza (1980), Bahlburg et al (1988, 1990), Gutiérrez‐Marco et al (1996), Toro and Brussa (1997), Monteros et al (1996), Toro et al (2003), Ortega et al (2011) and Toro and Herrera Sánchez (2019) provide information on the composition of graptolite faunas in this geological province. Middle Ordovician graptolite assemblages from other areas of the South American margin, including Bolivia, Peru and Colombia, were described by Bulman (1931), Lemon and Cranswick (1956), Mojica, Villarroel, and Macía (1988), Mojica, Villarroel, Cuerda, and Alfaro (1988), Mitchell et al (2008), J. Maletz et al (2010), Gutiérrez‐Marco et al (2012), Almanza (2017), Toro and Maletz (2018), and Gutiérrez‐Marco et al (2018), among others.…”